(a) Field of the Invention
The present invention relates to an automatic transmission. More particularly, the present invention relates to a method for reducing tip-in shock in an automatic transmission by limiting engine torque increase through limiting throttle opening when tip-in is detected.
(b) Description of the Related Art
A typical automatic transmission (AT) provides convenience in drivability by automatically shifting gears to a target shift-speed. For such a shifting operation, the AT firstly determines the target shift-speed depending on vehicle speed and throttle opening, and according to a map table of a predetermined shift pattern. The AT then operates various operational elements, such as an off-going clutch and an on-coming clutch, of a multiple speed gear mechanism included in the AT.
When tip-in (i.e., an abrupt hard operation of an accelerator pedal) occurs while a vehicle equipped with such an AT is coasting (that is, while it is under an inertial running in an idle state without operation of the accelerator pedal), the vehicle may experience a shock due to an abrupt increase of an engine torque, and such a shock is usually called tip-in shock.
While a vehicle is coasting, turbine speed in the transmission is typically higher than engine speed, that is, engine speed (Ne)<turbine speed (Nt). This is because the vehicle is not running by the power of the engine but by its own inertial momentum.
When the accelerator pedal is tipped-in in such a coasting situation, the engine speed abruptly rises above the turbine speed. The abrupt change of the engine speed from below the turbine speed to above the turbine speed implies that power transmission direction in a drive train of the vehicle is suddenly changed. In this case, the driver may feel a tip-in shock that is generated by backlash of the drive train.
Therefore, typically, when tip-in is detected during coasting of a vehicle, the ignition timing is dynamically retarded by a predetermined amount such that drive torque may be reduced in order to minimize the tip-in shock. However, the ignition timing retardation amount and the period of the retardation substantially influence responsiveness of acceleration. When the ignition timing retardation amount or the period of retardation is excessively small, torque reduction effect becomes negligible such that the tip-in shock may not be suppressed. When the ignition timing retardation amount or the period of retardation is excessively large, the shock may be reduced. However, in this case, vehicle acceleration may be delayed by an excessive reduction of the drive torque, or un-synchronized acceleration may happen.
In addition, typically, when tip-in is detected during a downshift in a coasting state, only the duty control of the hydraulic pressure of the on-coming clutch is adjusted depending on accelerator pedal operation. In this case, when an excessively large duty of the hydraulic pressure is supplied to the on-coming clutch, the engagement of the on-coming clutch becomes excessively early so as to thereby produce a shift shock.
In addition, when an excessively small duty of the hydraulic pressure is supplied to the on-coming clutch, the engagement of the on-coming clutch becomes excessively delayed such that the engagement thereof occurs only after a run-up so as to thereby also produce a shift shock in this case.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.